The overall purpose of this application is to support research investigating the costs of anti-microbial resistance. Long-term objective: To define the attributable cost of antimicrobial resistance for surgical site infections and bloodstream infections due to Staphylococcus aureus, so that investigators will be able to evaluate the cost effectiveness of proposed methods for the prevention of surgical site infections (SSI) and bloodstream infections (BSI) due to these resistant pathogens. Specific aims: i) To define the attributable impact of methicillin resistance upon economic costs of surgical site infections and bloodstream infections due to S. aureus. 2) To define the incidence and prevalence of surgical site infections and nosocomial bloodstream infections due to methicillin resistant S. aureus (MRSA) in a group of hospitals in the southeastern United States. Methods: The project will utilize 10 study hospitals and an infection control infrastructure that includes 3 physician epidemiologists and over 20 infection control practitioners. Patients with nosocomial bloodstream infections due to S. aureus and SSI are currently identified through prospective surveillance and have been and will continue to be prospectively entered into electronic databases at study hospitals. Additional study data will be obtained from patient charts and hospital databases. For the study of SSI, patients with SSI due to MRSA will be studied as cases and will be compared to patients with SSI due to methicillin susceptible S. aureus (MSSA) and to uninfected control patients who have undergone surgical procedures. For the study of patients with bloodstream infections, patients with BSI due to MRSA will be studied as cases and will be compared to patients with BSI due to MSSA and to uninfected control patients.